An assembly of devices that deliver a therapeutic radiation dose to an anatomical region from a single external radiation beam produced by a radionuclide source. A typical system is: 1) the treatment head (a shielded source vault containing a single radioactive source located in a moveable housing); 2) a rotating or fixed gantry with the treatment head at one end and a counter weight functioning as a beam stop on the other; 3) a collimator mechanism attached to the gantry to align the treatment beam; 4) a moveable patient table used to align and position the patient in the radiation beam; and 5) an operator's console containing the controls. It is commonly known as a cobalt therapy machine.